In a variety of integrated circuit (IC) fabrication processes, including plasma etching, plasma enhanced chemical vapor deposition (PECVD), and plasma sputter deposition applications, plasmas are produced within a process chamber by introducing a process gas at vacuum pressure into the chamber and then coupling electrical energy into the chamber to create and sustain a plasma in the process gas. The plasma may exist at various ionization fractions from 10−6 up to a fully ionized plasma.
Inductively coupled plasmas (ICP) are often used to produce high density plasmas, for example, for processes such as ionized PVD (iPVD) and some types of plasma etching. To generate such plasmas a coil or antenna is shaped and positioned with respect to the processing chamber to inductively couple energy into the processing chamber and thus create and sustain the plasma therein.
In some ICP systems, an inductive coil or antenna is positioned around or proximate the top portion or another end of the chamber to create a plasma within the chamber. Such an antenna is positioned on one side of a dielectric plate or window in the wall of the processing chamber, and electromagnetic energy from the antenna is coupled through the dielectric window and into the plasma. One suitable dielectric material for a window or chamber sidewall is quartz.
The geometry of an ICP system is a factor in determining both plasma density and uniformity, which, in turn, can affect the processing uniformity over the area of the substrate. It has often been regarded as desirable to produce a uniform, high-density plasma over a significantly large area so that large substrate sizes can be accommodated. Ultra large-scale integrated (ULSI) circuits, for example, are presently formed on wafer substrates having diameters of 200 mm and 300 mm.
Numerous coil configurations are used in inductively coupled plasma sources. Generally, these coils are becoming larger, requiring larger dielectric windows to allow RF energy to penetrate into plasma. Scaling up an external antenna for large area plasma in a conventional inductively coupled discharge meets such difficulties as thicker dielectric window to withstand atmospheric forces, and a higher inductance of antenna, significant increase of RF power. Problems also increase in the areas of stray capacitance, mutual coupling, voltage at the ends of scaled antenna, capacitive coupling between the antenna and plasma, sparking and arcing at atmospheric side among others.
The geometry of an inductively coupled plasma source, specifically of the antenna, is known to be a significant factor in determining both the plasma and processing uniformity. In an ICP source, plasma is excited by heating electrons in the plasma region near the vacuum side of the dielectric window by oscillating inductive fields produced by the antenna and coupled through the dielectric window. Inductive currents that heat the plasma electrons are derived from RF magnetic fields produced by RF currents in the antenna. The spatial distribution of the magnetic field is a function of the sum of the fields produced by each portion of the antenna conductor. Therefore the geometry of the inductive antenna and efficiency of RF power delivery into the plasma can in large part determine the spatial distribution of the plasma ion density within the reactor chamber.
In some cases, a Faraday shield that is transparent to the inductive component of the electromagnetic field is used to suppress the capacitive coupling from the antenna to the plasma and to prevent a conductive or other contaminating layer from building up on the dielectric window. The geometry and structure of such a shield have an effect on the spatial distribution of plasma inside the chamber as well.